This invention relates generally to silicon solar and photo cells, and more particularly the invention relates to a silicon cell with edge passivation and the method of manufacturing same.
The silicon solar cell is a well known device for use in converting radiant energy into electrical energy. See, for example, Swanson, U.S. Pat. No. 4,927,770, and Sinton, U.S. Pat. No. 5,164,019. As described in the Swanson patent, a silicon solar cell comprises a plurality of p and n conductivity type regions in a silicon body which generate voltage potential and a current when electron-hole pairs are created in a semiconductor body in response to impinging radiation, and the holes and electrons migrate to the p-doped regions and the n-doped regions, respectively. In a solar cell having interdigitated back surface contacts, the p and n regions are formed in alternating rows with a metal contact provided for contacting all doped regions in one row and with rows of like doped regions being connected in parallel.
Heretofore, small area solar cells having a surface area of less than 50 cm.sup.2 have been batch processed in an intrinsic (including lightly doped) single crystal silicon substrate by the selective diffusion of n+ and p+ regions in one surface of the substrate. The wafer is subsequently scribed and broken or sawed into a plurality of small individual chips or cells. Because small solar cells are normally sawed from a wafer after metallization, traditional high-temperature passivation techniques such as surface doping or thermal oxide growth cannot be used for edge passivation. Further, low temperature passivating films or coatings are less effective and are extremely difficult to selectively deposit on the sawed cell edges. Recombination of photogenerated carriers at the unpassivated edge surfaces can be a major current loss mechanism for high efficiency silicon solar cells, particularly for the small area solar cells.